FACTORS AFFECTING THE CONTROL OF WILD OATS IN RAPESEED WITH TRIFLURALIN

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Abstract
A series of experiments were undertaken to ascertain the effectiveness of trifluralin as a control of wild oats in rapeseed. Placement of trifluralin (a,a,a,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) in the soil was most important, as the main site of activity on wild oats (Avena fatua L.) was through the shoot or coleoptile. Polish rapeseed (Brassica campestris L.) was not affected by trifluralin up to 1.4 kg/ha regardless of placement. Activity was not seriously reduced by soil moisture as low as 10%, i.e., lower than air-dry soil. Activity was reduced by high soil organic matter and by incorporating the herbicide to depths below 7.5 cm. In field experiments, trifluralin sprayed in the spring at 1.12 kg/ha and tandem disced 7.5 cm deep immediately, resulted in upwards of 80% control of wild oats without injury to rapeseed. Yield increases depended on the density of the wild oats infestation. Bioassay showed a loss of approximately 90% of trifluralin activity in one growing season and cereals planted the year after trifluralin treatment were not affected. Spraying and incorporating trifluralin in October prior to seeding rapeseed the following May resulted in wild oats control nearly equal to that achieved by spring applications at both Lacombe, Alberta, and Melfort, Saskatchewan. This procedure has important practical implications in that it precludes the excess tillage and consequent soil drying associated with spring application.